A<tex>$+$</tex>78 dBm IIP2 CMOS Direct Downconversion Mixer for Fully Integrated UMTS Receivers

Abstract

The demanding dynamic range required by receivers for cell-phone applications makes the design of low-power fully integrated CMOS solutions extremely challenging. Commercially available third-generation (3G) products adopt a hybrid direct conversion architecture, where an inter-stage surface acoustic wave (SAW) filter between low noise amplifier (LNA) and mixer attenuates out-of-band interferers, alleviating linearity requirements set on the downconversion mixer. As a drawback, an off-chip component and an additional LNA are introduced, raising costs.Leveraging an in-depth analysis of second-order inter-modulation mechanisms in active downconversion mixers, this paper presents the design of a 0.18-m CMOS solution with outstanding linearity and noise performances. The input transconductor is RC degenerated, the output resistors are carefully matched and, most important, the parasitic capacitors at switching pair common sources are tuned out. Sixty samples from two distinct fabrication lots have been characterized. Minimum IIP2 is +78 dBm. For comparison, a second solution where inter-modulation products generated by the switching pair are not filtered out has been fabricated and tested. IIP2 values are always lower.Other measured performance results are: 16-dB gain with 4.5-MHz output bandwidth; +10-dBm out-of-band IIP3; 4-nVHz input referred noise voltage density while drawing 4 mA from 1.8 V.

A linearization technique for active mixers in zero-IF receivers with inherent balun

“…IIP2 or IIP3. In addition, some of them use an inductor which occupies a large silicon area and also has radiation effects on other parts of the receiver [3,4,5]. In the proposed techniques, both of the linearity parameters have been improved without needing any inductor.…”

Digitally Enhanced Alternate Path Linearization of RF Receivers

“…Furthermore, this technique does not require prior knowledge of one or more of the blocker frequencies, as do techniques that rely on the cancellation of TX leakage to meet the UMTS linearity specifications [15,16]. Although both IM2 and IM3 products can be concurrently canceled by parallel LMS adaptive filters, it was decided in this project to leverage recent work [17,18] in order to perform local IIP2 improvements so as to avoid adding additional analog-to-digital converters (ADCs) to the system to pass reference IM2 products.…”

Equalization of Third-Order Intermodulation Products in Wideband Direct Conversion Receivers

“…Furthermore, this technique does not require prior knowledge of one or more of the blocker frequencies, as do techniques that rely on the cancellation of TX leakage to meet the UMTS linearity specifications [12], [13]. Although both IM2 and IM3 products can be concurrently cancelled by parallel LMS adaptive filters, it was decided in this project to leverage recent work [14], [15] to perform local IIP2 improvements in order to avoid adding additional ADCs to the system to pass reference IM2 products.…”